Merchandise mark sensing system

ABSTRACT

A system for the automatic reading of prices, stock keeping units and and other like information, attached or affixed to packages and the like, and also providing pilferage control means. Responders, i.e, an array of microminiature resonant devices capable of storing and imparting information, are utilized in association with packages and the like for the storage of encoded information because of their ability to respond to certain microwave signals having a particular resonant frequency at a first plane of polarization and the further ability to reradiate signals to a receiver having a second plane of polarization, the or of the transmitted and received signal being the same. The polarization of the transmitted signals covering the frequency range of the responders provides a system in which a continuously transmitted signal may be utilized. Means are provided for initially polarizing and directing the microwave signals towards the responders and means of different polarization are provided for detecting the reradiated signals.

ll 1 ted States Patent Smith et al.

[ 1 Nov. 20, 1973 MERCHANDISE MARK SENSING SYSTEM lnventors: Richard C.Smith; William M.

Bechtold, both of Dayton, Ohio [73] Assignee: The National Cash RegisterCompany, Dayton, Ohio Primary ExaminerT. l-l. Tubbesing Attorney-LouisA. Kline et a1.

BUFFER BLANKING SWEEP POWER GENERATOR 4 AMPLIFIER [5 7 ABSTRACT A systemfor the automatic reading of prices. stock keeping units and other likeinformation, attached or affixed to packages and the like. and alsoproviding pilferage control means. Responders. i.e. an array ofmicrominiature resonant devices capable of storing and impartinginformation, are utilized in association with packages and the like forthe storage of encoded information because of their ability to respondto certain microwave signals having a particular resonant frequency at afirst plane of polarization and the further ability to reradiate signalsto a receiver having a second plane of polarization, the or of thetransmitted and received signal being the same. The polarization of thetransmitted signals covering the frequency range of the respondersprovides a system in which a continuously transmitted signal may beutilized. Means are provided for initially polarizing and directing themicrowave signals towards the responders and means of differentpolarization are provided for detecting the reradiated signals.

7 Claims, 9 Drawing Figures PAIEnTinunvzoms SHEU 1 BF 5 FIG.|

A/IZOO P-N JUNCTION CAPACITOR INVENTORS RICHARD C. SMITH 8 M/ WILLIAM M.BECHTOLD SWEPT SPECTRUM THEIR ATTORNEYS PAIEIIIEIIIM B 3.774.205

sum 2 or 5 FIG.4

DIELECTRIC MARKER 1 0' I" "I I AI LI I JW 1 RECEIVED SIGNAL I I I I I vI I I FIRST cLpcK PULSE INITIATED BY I l I I MARKER BIT I l I I I WSYSTEM INVENTORS B I I l CLOCK RICHARD c. SMITH a I I I I i wILLIAM M.BECHTOLD I l I "I" I I I I O I 754i I il I,. H M IQ,

I I I C I I I BY L GIC CONVERTER OUTPUT TI-IEIR ATTORNEYS PATENTEIJ3.774.205

SHEET 3 OF 5 BUFFER MEMORY INVENTORS RICHARD C. SMITH Bu WILLIAM M.BECHTOLD THEIR ATTORNEYS PATENTEI] NUVZO I975 SHEET 5 0F 5 THEIRATTORNEYS MERCHANDISE MARK SENSING SYSTEM BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to a merchandise marksensing system for the automatic reading of prices and stock keepingunits.

2. Description of the Prior Art The past several years have witnessedsubstantial activity in the design of systems in which the attaching ofa coded device onto an article facilitates the automatic reading ofinformation with regard to, or detection of, that article as it passes aparticular check-out point. More particularly, the coded device,attached to some article, in many cases contains price and inventorycontrol data. The coded device, as it passes by a specific point, e.g.,a check-out counter, in response to an interrogating signal, transmitsradio waves, light, or some type of intelligence carrying medium, to adetector which controls a cash register or similar device in response tothat intelligence and may transmit data to a computer for additionalpurposes, depending upon the system requirements.

One such system is described in U.S. Pat. No. 3,521,280 issued to Jancoet al. The .lanco patent discloses the use of coded lables containing aplurality of resonators, with each resonator being of a particularresonant frequency, wherein the presence or absence of a resonatorhaving a particular frequency provides one bit of information. Inoperation, interrogating signals, which cover a spectrum containing thefrequencies of the various resonators which comprise the coded label,are directed toward the coded label. The resonators transmit an outputsignal, when excited by energy of their particular frequency, to adetecting means. It is noted that in .lanco, it is necessary thatconducting materials be laid on both sides of a dielectric material inthe resonator.

U.S. Pat. Nos. 3,247,510, 3,493,955 and 3,500,373 are representative ofother systems utilized for identification of articles and for theprevention of theft of articles. U.S. Pat. No. 3,247,510 relates tomicrowave identification of railroad cars using a change of polarizationtechnique, and U.S. Pat. Nos. 3,493,955 and 3,500,373 relate to articletheft detection using electromagnetic radiation.

SUMMARY OF THE INVENTION The present invention relates to an improvedmerchandise mark sensing and memory interrogation system utilizingpolarization alteration techniques for the interrogation of informationencoded labels which comprise a plurality of L-C circuits havingparticular resonating frequencies. The system is characterized by theuse of microwaves to remotely access digital information attached tomerchandise, and by achieving this result in a serial access frequencydomain mode.

The system comprises four fundamental units, a readonly memory array,comprising a plurality of resonators, which are fastened to everyarticle, e.g., a piece of merchandise; a write unit (transceiver) whichencodes the read-only memory array with specific information including apilferage control bit; a read unit (transceiver) which reads the encodedinformation and which also destorys the pilferage control bit; andlastly, a pilferage control interrogation unit (transceiver) fordetermining whether an article has been properly checked out.

In operation, the read-only memory array is encoded with information.This may be accomplished prior to or after fastening the labels on thearticles. The labels are read at a check-out counter, which results inthe transmission of information to such devices as cash registers,computers, and the like. As the articles are carried out of the place ofbusiness, they are interrogated by the pilferage control unit whichtransmits radio energy of a particular frequency to the encoded label.However, there will be no response from the encoded array because theresonator associated with the pilferage control bit would have beendestroyed by the read unit, i.e., at the check-out counter.

The actual interrogation of a particular article may be accomplished byusing a pulse and listen principle. The interrogating transceiverprovides a fast falltime pulse of microwave energy at the frequency ofthe resonator under interrogation and then listens for the resonator toring, i.e., resonate at the interrogation frequency. It is necessarythat the receiver be blanked out during the transmission of theinterrogating pulse and listens (turned on) only after the transmitterhas been turned off. In this manner, the receiver is able to distinguishthe resonating signal from the transmitted interrogating signal.

An improvement found in the instant invention is the utilization ofpolarized transmitting and receiving antennas for polarizing themicrowave energy, thus obviating high frequency switching between thetransmitter and the receiver of the interrogating read unit which isnecessary when the pulse and listen principle is employed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of achip containing a plurality of L-C circuits.

FIG. 2 illustrates the sweep scale utilized in the instant invention.

FIG. 3 is an enlarged plan view of an L-C circuit as used in thisinvention.

FIG. 4 illustrates an alternate L-C structure, partially in section.

FIG. 5 illustrates a second alternate L-C structure, partially insection.

FIG. 6 is a block diagram of the write unit.

FIG. 7 is a timing diagram for the write unit.

FIG. 8 is a block diagram of the read unit.

FIG. 9 is a timing diagram associated with the read unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing,particularly to FIG. 1, there is shown a label 10 having, for purpose ofillustration, a cross sectional dimension of fifty mils and comprising aplurality of responders 12 which make up what has been previouslyreferred to as a read-only memory. The label 10, often referred to as achip, is shown as comprising 49 responders 12, although not limited tothis number, and is designed to be applied to articles such as, forexample, groceries, clothing, or the like by conventional means such asadhesives. The responders range in resonant frequency from 7.0GHz to 11.9GHz. The 49 responders are separated from each other by a differenceof nominally MHz in the illustrated embodiment and no two respondershave like resonant frequencies. It should be noted that no specificamount of difference is necessary, and that the differences need not beequal, so long as the differences are of predetermined magnitude.

The read-only memory is a standardized array of microminiature resonantdevices (such as L-C tank" circuits, referred to as responders)progressively tuned across a wide frequency spectrum. Throughout thisspecification, the terms L-C circuits and "responders" are usedinterchangeably. The system may utilize some part of the device (such asthe inductor in the L-C circuit) as an antenna. A given device is madeto resonate and reradiate energy by remotely exicting it with a pulse ofenergy at its own natural resonant frequency.

Two of the methods by which devices such as L-C circuits can bedestroyed are by shorting the capacitor or opening the inductor. Thelabel is remotely encoded with information by overdriving selectedresponders 12 with an excitation pulse which induces an RF current in aselected resonating device larger than that which the device can carry,thereby destroying" it such that it will respond when interrogated by asignal of its own natural frequency.

Each responder 12 thus represents a bit of information. Those circuitswhich are complete, i.e., not destroyed, and which resonate within theiroperating frequency range, may be assigned the value of logical ones"and those circuits which are not complete and which resonate outside ofthe operating frequency range may be assigned the value of logicalzeros.

One of the responders I2 is allotted for pilferage control and will bedestroyed" by overexcitation during the normal process of merchandisecheck-out. All merchandise is interrogated at a pilferage controlfrequency by a transceiver at each exit. If any piece of merchandise isnot checked out properly, the device will remain active and willresonate when interrogated by a signal having a frequency identical tothe natural resonant frequency of the pilferage control responder. Theresponse sensed by the receiver drives an alarm or other signalingdevice to indicate pilferage.

Because of the nature of the processes used to fabricate an aray of suchdevices, it is generally easier to control the separation of theresonant frequencies than it is to control each precise resonantfrequency. More specifically, due to the batch nature of processing,i.e., manufacturing, L-C circuits, the dielectric thickness, dielectricconstant, capacitance and inductance crosssection may vary from batch tobatch, but not significantly across a 50 mil chip. Therefore, because ofthis processing phenomenon, each responder 12 will not necessarily be ofthe specified design resonant frequency. For example, the designfrequencies of responder 1212a, ll2ba and l2gg might be designed to b7.0GHz, 7.1GHz and l l.9GHz respectively. However, in actuality, thenatural frequency of responder 120a might be 7.0GHz .OOIGHz. Similarlyresponder 121m might be 7.1GHz 1 .OOlGHz. Therefore, it can be seen thatif the frequency were critical, many of the batch processed L-C circuitswould, of necessity, be discarded. However, it has been discovered thatalthough there might be a variance in the natural resonant frequency ofeach responder, the variance in each L-C circuit will be approximatelythe same and in the same direction, i.e., the frequency differencesbetween L-C circuits will be nearly equal. To be specific, if the actualfrequency of responder l2aa were 7.00lGHz, which is 0.00lGHz greaterthan the design frequency of 7.000Gl-Iz, the probability is very greatthat the natural frequency of responder 1217a is 7.l0lGI-Iz, also 0.001greater than the design frequency of 7.100GI-Iz. It can thus be seenthat while the actual natural resonant frequency might vary from thedesigned frequency, that the frequency differences between responderswill be approximately the same. It would be prohibitive in cost toattempt to control the processed resonant frequency of the L-C circuitswithin i lOMI-lz. Since the difference in frequencies between theresponders is approximately the same, a sliding frequency scale forencoding and interrogating is used because the absolute magnitude of theresonant frequency is not the important parameter, but what is criticalis that each resonant frequency of the L-C circuits on the chip be MHzapart.

Each memory array contains a greater number of devices than are requiredto hold the required data i.e., the resonant frequencies are designed toextend beyond both limits of the operating frequency range. To locatethe first bit within the operating frequency, the transceiver beginssweeping up from the beginning of the range until it detects the firstdevice whose resonant frequency lies within this range. This firstdevice is called the marker bit" (FIG. 2) and its correspondingfrequency is the marker frequency. If the resonant frequencies of thearray are separated by an interval Af, 100MHz in this instance, thenthis marker frequency must lie within Af Hertz of the beginning of thefrequency range. The transceiver subsequently interrogates in steps ofAf, beginning with the marker frequency. The sliding frequency scale isused in the writing process in a similar way.

FIG. 3 illustrates, in greater detail, a responder 12 such as shown inFIG. 1. The responder 12 comprises a microstrip of a metallized inductor14, having a rectangular configuration, the length of which may, in atypical embodiment, range from 3 to 10 mils. The open ends thereof areconnected to a p-n junction capacitor 16, thus forming what is oftenreferred to as an L-C tank circuit. The responder 12 is formed on asubstrate 18 such as a passivated silicon substrate, by conventionalmetal deposition or etching techniques. The thickness of this substrate,in a typical embodiment, may be 2 to 4 mils. This type of resonator willhave a Q of 1-10 at X-band frequencies.

FIG. 4 illustrates an alternate from of a responding circuit comprisingan inductor 13 having a rectangular configuration and terminated in aseries of interdigitated fingers. This type of responder may befabricated by etching copper clad Mylar. The terminated interdigitatedfingers are shown coated with a dielectric to increase the capacitance.

FIG. 5 illustrates yet another form of a responding circuit comprising athin film inductor 17 having a rectangular configuration. The capacitorcan be fabricated by growing an oxide such as cupric or chromic over theinductor 17, then adding a conductor 19.

FIGS. 6 and 7 illustrate a functional block diagram of the write" unitand the associated timing diagram respectively. A conventional manualkeyboard 20 is connected to a conventional buffer memory 22 which may beof the solid state type. The buffer memory 22 receives an input from aclock 24 and has an output connected to a blanking circuit 26, which hasan output connected to a sweep generator 28, which in turn is connectedto outputs from the clock 24 and a sweep controller 30. The sweepgenerator 28 provides an output to a variable controlled oscillator(VCO) 32 which in turn is connected to a power amplifier 33. Atransmitting antenna 34 is coupled to the power amplifier 33. Areceiving antenna 36 is coupled to a receiver 38, the output of which isconnected to the sweep controller 30. The sweep controller has twooutputs, one of which is connected to the clock 24 and the other to thesweep generator 28.

During the writing operation, i.e., the encoding of the label 10, themanual keyboard 20 is used to input the desired information into thebuffer memory 22 in the form of bits having assigned values of logical lor 0. To begin the actual writing, the controller 30 sweeps the VCO 32across the operating frequency spectrum with an attenuated output inorder to prevent damage to the responders 12. The sweep continues insmall finite steps until the receiver 38 detects the marker frequencybit (waveform A of FIG. 7). The marker frequency is transmitted by thefirst L-C circuit which responds to the swept transmitted signal. At thetime of reception, the clock 24 is actuated (waveform B of FIG. 7),which results in serially shifting out of the buffer memory 22 (waveformC of FIG. 7) any information which is to be written into the label 10.The clock 24 also pulses the sweep generator 28 which directs the VCO 32to transmit amplified microwave energy (waveform E of FIG. 7) towardsthe label at a magnitude sufficient to destroy an L-C circuit, ifrequired in accordance with the information stored in the buffer memory22. For example, let it be assumed that the first bit in the buffermemory 22 is a zero (waveform C of FIG. 7). The VCO power voltage(waveform D of FIG. 7) for this period of time is at a magnitude greaterthan that required for reading. Therefore, an L-C circuit responding tothe particular frequency transmitted at this point in time will bedestroyed. Thus when sensed at some later time, this destroyed L-Ccircuit will not respond, which in this system designates a zero.

The frequencies transmitted are adjusted to align with those of theresonators by properly choosing the values of the clock and sweep rates.The information stored in the buffer memory 22 determines the operationof the blanking circuit 26, i.e., 1 bits energize the blanking circuit26 which prevents the pulsing of the VCO 32, so that the L-C circuitassociated with the frequency which was to have been transmitted at thatpoint is not destroyed, while 0 bits have no effect on the blankingcircuit. Thus, ifa particular bit frequency represents a 1, itscorresponding resonator in the read-only memory array is unaffected bythe write unit and will therefore respond when interrogated by the readunit, as will subsequently be explained.

FIGS. 8 and 9 illustrate the interrogating unit, i.e., the read unit andthe associated timing diagram respectively. A clock 60 is connected to asweep generator 62 which receives a signal input from a sweep controller66. The sweep generator 62 output is connected to a variable controlledoscillator (VCO) 64 which in turn is connected to a power amplifier 40,and the output of the power amplifier 40 is coupled to a polarizingtransmitting antenna 42 which may be a conventional slot antenna. Areceiving antenna 52 which is polarized in a different orientation thanthe transmitting antenna is coupled to a receiver 50 having two outputsrespectively connected to the sweep controller 66 and a logic buffer 46.The logic buffer 46 is connected to a utilization device 44 such as, forexample, a cash register. The logic buffer may comprise a conventionaldiode tree and a storage register.

In operation, the interrogation unit is positioned at some check pointthrough which the articles must pass. The VCO 64 is controlled by thesweep generator 62 and the clock 60 in the transmission of microwaveenergy across a frequency scale at intervals of Af. The microwave energyis polarized by the antenna 42 which may be a slotted antenna polarized,for example, in a vertical direction. Any L-C responder 12 whichreceives microwave signals at its natural resonating frequency, whetheror not that signal is polarized, will in turn reradiate energy. Thisreradiated energy will not have any particular polarization but willcontain energy of all possible polarizations. The receiving antennawhich may be a slotted antenna and polarized, for example, in ahorizontal plane, will receive only signals having a horizontal plane ofpolarization. Therefore it can be seen that there can be no interferencebetween those signals transmitted from the antenna 42 and those receivedby the antenna 52. Referring to waveform A of FIG. 9 it can be moreeasily seen that upon the reception of the marker pulse, the clock 60 isset in operation resulting in the transmission of energy in MHz steps(waveform B of FIG. 9). It can be seen (waveform A of FIG. 7) that theabsence of energy indicates a 0 bit of information and the presence ofreceived energy indicates a 1 bit. The received signals are coupled tothe conventional logic buffer 46 where they are temporarily stored andconverted into signals capable of being utilized by the utilizationdevice 44 (waveform C of FIG. 9).

As was mentioned earlier, one responder 12 on the label 10 is reservedfor the purpose of pilferage control, which responder is destroyed atthe interrogating station by a transmitter which overdrives it. This maybe done under manual control or it may be programmed. In order to bestutilize the present invention, it is necessary to establish pilferagecontrol interrogators at each point of egress from the establishment.The pilferage control interrogator is not shown since it would besimilar to the interrogator unit of FIG. 8 with the exception that asignal having only one frequency need be transmitted, namely the naturalfrequency of the L-C responder 12 which is chosen as the pilferagecontrol bit. The receiver of this unit would receive no signals if thepilferage control bit were destroyed by the interrogating station at thecheck-out point. However, if this were not the case, the receiver wouldgenerate a signal which could be used to sound an alarm or otherindicating device.

The invention described here illustrates a system in which amicrominiature device may be remotely read, independent of orientation,and with wide tolerance with respect to depth of field and skew. Thetransmitter in the illustrated embodiment would require an operatingspectrum of 7.0 to 12.1 GI-Iz with a frequency separation of 100MHz anda maximum power level of l00mw. The pulse width could be from 5 to 10microseconds. The receiver would require an operating spectrum of 7.0 to12.0GI-I2.

What is claimed is:

l. A sensing system comprising: a transistor for generating outputmicrowave interrogation signals in predetermined increments over apredetermined frequency range and at a predetermined magnitude;

a first antenna polarized in a first direction and coupled to saidtransmitter such that all transmitted microwave signals have one initialplane of polarization;

a plurality of responder circuits, each responsive to certain of saidtransmitted microwave signals, and each having a particular naturalresonating frequency and separated by a predetermined difference fromany other resonating frequency, each responder circuit being capable ofreradiating microwave energy containing substantially all possibleplanes of polarization at its natural resonating frequency;

a second antenna polarized in a second direction capable of interceptingand detecting that portion of reradiated energy having a plane ofpolarization in said second direction;

means coupled to said second antenna for developing electrical signalsin conformance with those intercepted by said second antenna; and

memory means for storing said developed electrical signals.

2. A system according to claim 1, and also including a utilizationdevice responsive to said electrical signals stored in said memorymeans.

3. A system according to claim 1 wherein each responder circuitcomprises a single turn inductor terminated in a pm junction capacitor.

4. A system according to claim 1 wherein each responder circuitcomprises a rectangular single turn inductor with side dimensionsranging from 3 to 10 mils.

termined frequency MHz.

nals in steps differing by predetermined frequency increments over apredetermined frequency range and predetermined magnitude;

a first polarized antenna coupled to said transmitting device such thatall transmitted microwave signals are polarized in a first direction;

an encoded read-only memory, responsive to said transmitted microwavesignals, and formed by a plurality of LC circuits, each L-C circuithaving its own particular natural resonating frequency and eachresonating frequency being separated from at least one other resonatingfrequency by a frequency difference of said predetermined frequencyincrement, said resonating circuits being capable of reradiating signalscontaining substantially all possible planes of polarization;

a second polarized antenna capable of receiving only that portion ofreradiated energy polarized in a second direction;

receiving means coupled to said second antenna for receiving energydetected by said second polarized antenna;

means for converting energy received by said receiving means into logicsignals; and

a utilization device for said logic signals.

7. A system according to claim 6 in which said predeincrement isapproximately UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. L77L2Q5 Dated N h 2Q 1913 e fls) Richard 0. smigh & Williamgechtold It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 1, delete "transistor" and substitute --transmitter--.

Signed and sealed this ll th day of May 19714.. 1

' '(sEAL) Atte st: I EDWARD M.FLE'I'CHER,JH./ c.- MARSHALL DANN oCommissioner of Patents Atte sting "Officer 7 LISCOMM-DC OOSTQ POO FORMPO-IQSO 10 69) UNITED STATES PATENT OFFICE y CERTIFICATE OF CQRRECTIONPatent No. 3 77 2() 5 Dated N h 2Q 1213 mvencms) Righard c. Smith &William m. fiechtold.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 7, line I, delete "t'ransistorwand substitute --transmitter--Signed and sealed this 114th day of May 19711..

I (SEAL) Attest: r EDWARD M.FLETGHER,JR.J T c. MARSHALL DAMNAttesting'Officer I T j Commissioner ofPatent s' FORM po-xgso (lo-9s LIICOMM DC 037 MP0

1. A sensing system comprising: a transistor for generating outputmicrowave interrogation signals in predetermined increments over apredetermined frequency range and at a predetermined magnitude; a firstantenna polarized in a first direction and coupled to said transmittersuch that all transmitted microwave signals have one initial plane ofpolarization; a plurality of responder circuits, each responsive tocertain of said transmitted microwave signals, and each having aparticular natural resonating frequency and separated by a predetermineddifference from any other resonating frequency, each responder circuitbeing capable of reradiating microwave energy containing substantiallyall possible planes of polarization at its natural resonating frequency;a second antenna polarized in a second direction capable of interceptingand detecting that portion of reradiated energy having a plane ofpolarization in said second direction; means coupled to said secondantenna for developing electrical signals in conformance with thoseintercepted by said second antenna; and memory means for storing saiddeveloped electrical signals.
 2. A system according to claim 1, and alsoincluding a utilization device responsive to said electrical signalsstored in said memory means.
 3. A system according to claim 1 whereineach responder circuit comprises a single turn inductor terminated in ap-n junction capacitor.
 4. A system according to claim 1 wherein eachresponder circuit comprises a rectangular single turn inductor with sidedimensions ranging from 3 to 10 mils.
 5. A system according to claim 1wherein each responder circuit comprises a single loop inductorterminated in a series of interdigitated fingers coated with adielectric.
 6. A sensing system comprising: a transmitting device fortransmitting microwave signals in steps differing by predeterminedfrequency increments over a predetermined frequency range andpredetermined magnitude; a first polarized antenna coupled to saidtransmitting device such that all transmitted microwave signals arepolarized in a first direction; an encoded read-only memory, responsiveto said transmitted microwave signals, and formed by a plurality of L-Ccircuits, each L-C circuit having its own particular natural resonatingfrequency and each resonating frequency being separated from at leastone other resonating frequency by a frequency difference of saidpredetermined frequency increment, said resonating circuits beingcapable of reradiating signals containing substantially all possibleplanes of polarization; a second polarized antenna capable of receivingonly that portion of reradiated energy polarized in a second direction;receiving means coupled to said second antenna for receiving energydetected by said second polarized antenna; means for converting energyreceived by said receiving means into logic signals; and a utilizationdevice for said logic signals.
 7. A system according to claim 6 in whichsaid predetermined frequency increment is approximately 100MHz.